sulfur resistance of bi-metallic Ni catalysts

在许多应用领域，由于硫中毒金属表面而导致的催化剂活性的丧失是有问题的。这方面的例子包括将生物质转化为液体燃料和化学品，催化还原柴油中的高级多芳烃，以及固体氧化物燃料电池的运行。因此，提高多相催化剂的抗硫性是非常有意义的。本项目的目的是验证一个假设，即金属催化剂的电子能带结构的改变可以导致抗硫性的提高。这应通过将一种贱金属与另外两种成分合金化来实现。文献检索得到了两种特别感兴趣的镍合金，它们将作为模型系统进行研究。其中一种是Ni-Ru，理论上给出了费米能级上态密度的变化和S吸附的变化。第二个体系是Ni-Sb系，实验表明其抗S性能有很大提高，但找不到机理解释。对于这两个体系，应利用在线表征方法和气溶胶系统提供的良好的颗粒结构可能性来研究硫对催化性能的影响和失活机理。从项目目标的定义来看，结果是三个核心问题：硫的吸附如何依赖于合金颗粒的组成；合金金属颗粒的电子结构如何随着组成的变化而变化？在有硫存在的情况下，试验反应的催化活性是如何随时间变化的，并作为颗粒组成的函数？实验过程可以分为三个步骤。第一步将包括产生大小和成分可控的二元合金颗粒，并对其进行仔细的表征。对于后一种方法，将使用在线气雾剂方法，但另外还将使用离线工具。一个核心的在线工具将是气溶胶光电子能谱(APES)，它允许表征颗粒的电子结构。在第二步中，将研究硫磺在颗粒表面的吸附，这在一定程度上也依赖于类人猿。第三步将重点研究这些结构的催化活性以及它们的抗硫性与颗粒组成的关系。

The loss of catalytic activity due to poisoning of metallic surfaces with sulfur is problematic in many areas of application. Examples for this are the conversion of biomass into liquid fuels and chemicals, the catalytic reduction of higher polyaromatics in diesel fuel and the operation of solid oxide fuel cells. An increase of the sulfur resistance of heterogeneous catalysts is therefore of great interest.The aim of the proposed project is the testing of the hypothesis according to which a change in the electronic band structure of a metal catalyst can lead to an increase in sulfur resistance. This shall be accomplished by alloying a base metal with two other components. Literature search yielded two Ni-alloys of particular interest, which will be investigated as model system. For one this is Ni-Ru, for which a change in the density of states at the Fermi-level and at the same time an alteration of S-adsorption were theoretically shown. The second system is Ni-Sb, for which a strong increase in S-resistance was experimentally shown but no mechanistic explanation could be found. For both systems the effect of sulfur on the catalytic properties and the mechanisms of deactivation shall be studied making use of online characterization methods and the excellent possibilities for particle structuring offered by aerosol systems.From the definition of the project goals three core questions result:How does the adsorption of sulfur depend on the composition of alloyed particles?How does the electronic structure of alloyed metal particles change with composition?How does the catalytic activity of a test reaction change with time in the presence of sulfur and as a function of particle composition?The experimental procedure can be organized in three steps. The first step will comprise the generation of binary alloyed particles of controlled size and composition, which will be carefully characterized. For the latter online aerosol methods but additionally offline tools will be employed. A core online tool will be aerosol photoemission spectrometry (APES), which allows the characterization of the electronic structure of the particles. In a second step sulfur adsorption on the particle surfaces will be investigated, also relying in part on APES. The third step will focus on the investigation of the catalytic activity of the structures and their sulfur resistance in dependence on particle composition.